1. Field of the Invention
This invention belongs to the technical field of reducing the weight and increasing the strength of the fiberglass reinforced plastics (FRP) bumper reinforcement for vehicles such as automobiles that functions as a backup beam member for an elastic bumper.
This invention relates to the FRP bumper reinforcement structure for vehicles: which is mounted laterally on the front and rear of the vehicle such as automobile as a backup beam member for supporting an elastic bumper consisting of an urethane foam core member and an urethane elestomer crust member fitted over the urethane foam core member; and which is rectangular in cross section and has at least one horizontally extending reinforcement web between the top and bottom plates thereof. And more particularly, this invention relates to the bumper reinforcement structure for vehicles in which forwardly projecting strips are formed on the front wall of the bumper reinforcement at intersections between the front wall and the top and bottom plates as well as the reinforcement web.
2. Description of the Prior Art
As is known, the front and rear of automobiles are fitted with a bumper as a safety means. For improved safety, light weight and improved fuel efficiency, an increasing number of elastic bumpers are being used which consists of an urethane foam core member and an urethane elastomer crust member fitted over the core member.
The bumper reinforcement as a backup beam member which supports the elastic bumper has conventionally been made of metal and formed into a closed shape in cross section. To reduce the weight and increase the shock absorbing capacity and the fracture strength, the bumper reinforcement that is formed by pultrusion process from fiberglass reinforced plastics has come to be used on wide scale.
That is, as shown in FIGS. 1 and 2, the elastic bumper 3 consisting of the urethane foam core member 1 and the urethane elastomer crust member 2 fitted over the core member 1 is mounted to the FRP pultruded bumper reinforcement 6 by fixing it to the bracket 4 of the bumper reinforcement 6 with bolts 5.
The bumper reinforcement 6 which is closed in section and extends linearly or curved is mounted laterally. The bumper reinforcement 6 has between the top and bottom plates 7, 8 thereof one to three horizontally extending reinforcement webs 11 connecting the front and rear walls 9, 10 so as to prevent the front wall 9 from being broken when applied with an impact load, without increasing the weight of the bumper reinforcement.
However, since the fiberglass reinforced plastics, from which the bumper reinforcement 6 is formed, consists of a one-way glass roving (60-80%) and, as matrix resin, unsaturated polyester resin, epoxy resin and vinyl ester resin, it has a conspicuous characteristic of anisotropy. That is, the bumper reinforcement has a reasonably high tensile strengh in the direction of the fiber orientation; however, the tensile strength in the direction perpendicular to the fiber orientation is low. This is frequently observed with the product formed by pultrusion process from the fiber reinforced thermosetting resin. Due to this anisotropy characteristic of the pultruded fiberglass reinforced plastics, the bumper reinforcement has not sufficient rigidity and is easily deformed. Therefore, although it has a reasonably high tensile strength in lateral direction, it is very likely that the bumper reinforcement will easily be broken when an excessive impact load is applied from the front wall 9. Particularly the intersections 12, 13, 14, 15 between the front wall 9 and the top and bottom plates 7, 8 and the reinforcement webs 11 are susceptible to fracture because stress concentration will occur at these intersections when impact load is applied.
This is verified by the experiments using actual bumper reinforcement which showed that the actual strength of the bumper reinforcement is much lower than the estimation calculated from the bending strength of the test piece.